[NSRCA-discussion] Electric vs. Glow

[Ed Alt]

Bob:
I think so too, i.e., there are likely some good RPM ranges where braking will be more effective and you can grab regen power to freshen the cells if wanted.  I don't think it's a bad idea at all, it's a great idea.  I'm just thinking that it's not a simple problem to get it optimized and that we have to balance several factors.  Just like everything else we tackle in this hobby, it's what makes it fun to try to do it.

Ed
  ----- Original Message ----- 
  From: Bob Richards 
  To: NSRCA Mailing List 
  Sent: Monday, February 20, 2006 7:23 AM
  Subject: Re: [NSRCA-discussion] Electric vs. Glow


  Ed,

  Ok, I'll buy that. Taken to the extreme, a non-spinning prop will have less drag than one that is windmilling.  I would think that there is a point where the braking is at a maximum (rpm/mph) and perhaps this would be free spinning, but my gut tells me there is some amount of resistance that could be added to the prop before this maximum is reached.  And this point would be different depending on the prop used. This reminds me of the old 4C vs 2C engines, the 4C is supposed to (does?) have more "braking" in down lines.

  Also, the props we use are not designed for reverse lift -- like a flat bottom airfoil flying upside down. They may be -- and probably are -- stalled when trying to add resistance over freewheeling.

  Bob R.


  Ed Alt <ed_alt at hotmail.com> wrote:
    Bob:
    The faster the prop turns in a freewheeling mode, the more braking effect, so the less load on it from expending energy into a load, the faster it will turn.  When you have an electrical generator being propelled by some force and the voltage generated from the windings is not connected to an external load, then no current other than eddy currents is going to flow in the motor, which ought to be fairly insignificant.  So there is an EMF, but no significant power generated by the motor windings when being driven by an external mechanical force when there is an incomplete circuit from the windings into any external electrical load.  

    Ed



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